Remote tuning system for radio receivers



July 7, 1936. A. A. THOMAS REMOTE TUNING SYSTEM FOR RADIO RECEIVERS 3sheets-sheet 1 Filed April 30, 1930 Y July 7, 1936. A. A. THOMAS REMOTETUNING SYSTEM FOR RADIO REGEIVERS Filed April 30, 1930 3 Sheets-Sheet 2NVENTOR July 7, .1936. A. A; lTHOMAS REMOTE TUNING SYSTEM FOR RADIORECEIVERS Filed April 30{ 1950 5 Sheets-Sheet 3 Patented July 7, 1936 UN'T E D.: S

PATENT cerros REMOTE. TILNDG SYS'IEM'.v FOR, RADIO.

RECEIVEBQS' Application April 30.11930; seriarNo. 448.465-

12 Claims.

My invention relates to the art oltuning .radio receivers from adistance, and its object is to provide a remote tuning systeinof simpleconstruction and reliable operation. Forthis purpose I' instal in. theradio` cabinet an electromagnetically balanced circuit arrangement-foroontrollinga A manuallyadjustable station indicatonin the?.

remote tuningl devicedetermines the positicnjof` the associatedrheostatarm and thereby. controls.. the, strength ofcurrentpassinglthrough the connected coil of the differentialrelay..vVilhentlfie.A

relay circuits are closed afterv theoperator has selectedv a desiredstation, one of thevtwoy coils..

will overbalance the. other and the. ,moto1 t switch.

isclosed. The tuning. shaft. moves theconnectedv rheostat arm until the.currentthrough theiasso: ciated .coil ,counterbalancesthe eiect. ofthere. motely controlled coil,v whereupon.. the motor.. switch is openedand the. tuning-shaft;stops.in-l stantly in correct position fortheselected. station. The electric motor always runs in the samedirecf.tion, so that only a single switchisneeded for the differential relaylto closev andbpen` thesame circuit.v Another advantageA 0i a...l10n-reversible. motor lies in the fact that auniversalv motorola.,-erating` oneither A.. C. or D. C.l houseflighting- ClTCutS maybe used.

The remote tuningA device otmyinvention coni-y prises a small box..containing. only' one. or two.. switches, a rheostat, a, volumecontrohand per haas also .asienal lamp. although the latter is. notnecessary. In a preferred form oflmy inven-v tion.. I use azsingle,rheostat resistance to` perform a double` function; controlling .thecurrent through one of the differential relay coils\.for selecting a.station, and .controlling theA volume. of l. reproduction. This twofoldoperation of. the rheostat is Controlled by a single lmob ontop. of .thebox., The. knob. .is rst rotatedtoA move arl indicator. to the. desiredstation mark. and then the knob. is pushed.' into close. the` circuits.of the relay. coils.. When the., selected station is .in tune, theknolofis. re.-

leasedjand may now. be turnedgto regulate the volume. Inothervwords, asingle knob performs the triplepunction of .selecting a station, closingthe` relay circuits in the receiver, and controlling the loudspeakervolume. The only other nger 5 piece needed on the control boxis a switchmember forr turin'ng. the electric. power onv and off'. The control" boXis operatively connected with the radio cabinet by an electriccablecontaining` only a few wires of low voltage. Inlone embodiment 1o.of: my invention, not-more thansix wires are l needed in the cablefoiicomplete controlof the receiver.

The practical advantages andv novel ,featuresof' my remote controlsystem will'be understood from l5l a. desriptaof. the accompanying.drawings. in which Fig. 1 is asirnplied diagram of circuitconnec.- tionsillustrating `the principle of operationof my invention; a.

Fig- 2"is a. top. view of the. remote control box;

Fig. 3-shows a transverse section through the box on line; 3-301 Fig. 2;

Figs. 4 land 'represent sectional plan views on lines 4'-.-4- and5-f,.-5;j respectively, of Fig. 3;

Fig, 7.is a. fragmentarysectional view online 1-1 of Fig. 4;

Fig. 8--is a. topplan viewof thetuning mechanism inthe radio cabinet;`

Fig. 9illustrates a Afront elevation of the tuning mechanism,l partlysectioned, on lirie` 9 -9 of f Fig". 8*;

Fig. 10-1isa vertical section through line Ill- I0 afrit... 9*:

Fig. 11-is a detached perspective ofthe insu-4 latingblockthatsupportsthe relay switchesof the. remotel control system;

Fig. 12 shoiwsa fragmentary View of the insulatingwblockpartly sectionedon line I 2-I 2vvv of .40 Fig! 8.,.. l

Fig; 13 is a diagram of circuit connections be.- tween the tuning shaftand remote control box;

Fig. leinustratesa modified nsystem of volume' control; Iand j 45 Fig;l5` showsY diagrammatically another form ofdifferential relay and'associated switches for controlling thentunving shaft.

' I- shall'first explain the underlying. principle,

of'myjinvention by referringtohFig. 1, which shows 50aesimplifledgdiagram of circuit connections and is; notintendedito..represent .a complete system such ashwoul'd bauscdin actualiprratice.An elec.- tric. motor llljin the .radio cabinet. isoperatively`connected with a shaft Il*whichcarriesv (or other- 55.

wise controls) suitable tuning elements I3. These are diagrammaticallyindicated as variable condensers, which are almost universally employedfor tuning purposes in modern radio receivers. It is assumed that themotor I9 drives the tuning shaft I2 at the requisite low speed, andautomatic reversing mechanism may be interposed to reverse the rotationof the shaft at each end of the dial. A rheostat R has a rotary contactarm I4 movable in unison with tuning shaft I2, either by being directlymounted thereon, or being otherwise connected thereto in any practicalway. The resistance element I5 of the rheostat is connected at one endto a solenoid coil I6 which is connected to one side of battery II. Theother side of the battery is connected to the movable contact arm I4. Asecond coil I 8 is connected at one end to the resistance element I9 ofa rheostat R in the remote control box, and the other end of the coil isconnected to one side of a battery 20. The other side of this battery isconnected to the rotary contact arm 2I of rheostat R.

The solenoid coils I5 and I8 are arranged in axial alignment and controla movable magnetic core or armature 22 which is mounted on a lever 2Spivoted at 24. The movements of the magnetic core 22 control a switchcomprising a fixed contact 25 and a movable contact 26, which is mountedon (or otherwise connected to) the pivoted lever 23. The xed contact 25is so shaped that it is engaged by the movable contact 25 when themagnetic core 22 is drawn into either of the coils I6 and I8. Acontracting coil spring 21 normally holds the core 22 centrally of thecoils, so that contact 25 is separated from the xed contact 25. Thesetwo contacts constitute a normally open switch in the circuit of motorID, which is connected to a battery 28. The rheostat arm 2I in theremote control box is operated by a knob or other suitable finger pieceand an indicator on the box enables the operator to select a desiredstation. In Fig. 1 the stationselecting scale or dial isdiagrammatically indicated at 29, and the rheostat arm 2I may be assumedto correspond in position to the indicator arm on the control box.

Let us suppose that the switches 3S and 3I are closed and that therheostat arm 2I has been moved to the position shown in Fig. 1 fortuning in a certain station. Unless the tuning shaft I2 of the radioreceiver happens to be in tuning position for the selected station, therheostat arms I4 and 2I will occupy diierent positions, so that thecurrent through one of the solenoid coils I6 or I8 will be stronger thanthe current in the other coil. Consequently, the predominating coil willdraw in the iron core 22 and move contact 26 against contact 25. Themotor circuit is now closed and the tuning shaft I2 is operated in onedirection or the other until the rheostat arm I4 so adjusts the currentin coil I6 that the electromagnetic effects of the two coils arebalanced or neutralized. When that occurs, the core 22 assumes itsnormal or neutral position and opens the motor switch 25-26, so that theshaft I2 stops in correct tuning position for the station selected bythe operator from the remote control box. The solenoid coils I6 and I8and the resistances I5 and I9 are so designed that for any position ofrheostat arm 2| the opposing electromagnetic eiects of the solenoidcoils are neutralized when the radio shaft I 2 is in tuning position forthe selected station. It is immaterial which of the two coilspredominates when they are rst energized, because the movement of thecore 22 in either direction from its neutral position causes the motorswitch 25-26 to be closed. The switches 35 and 3| are normally open andclosed simultaneously from the remote control box, as will be explainedlater in detail. The batteries II, 20 and 28 in Fig. 1 are shown asseparate sources of current to simplify the circuit diagram, lout inactual practice the electric power for the remote control circuits isderived from a single source, which may be the houselighting system.

Figs. 2-'7 show the construction of one form of remote control box whichcomprises a cylindrical body 32 closed by aremovable cover 33. One wayof fastening the cover in place is to provide it with an annular flangeor shoulder 34 adapted to receive fastening screws 35 from the side, sothat they do not show on top of the box. The box sections 32 and 33 maybe made of sheet metal or molded of insulating material like hardrubber, bakelite, ber and others. The resistance element I9 of rheostatR is shown as a fine wire wound on a semi-circular strip 36 which issecured at its ends in a pair of blocks 31 attached to the box in anypractical way, as by screws 33. The strip 36 is preferably of flexibleinsulating material, so that it is normally straight to permit windingof the wire by machine. The wire-wound strip is bent into a semi-circleso that the ends can be inserted in slots 38' of blocks 31 and securedby screws or otherwise. Instead of a resistance wire I may useresistance material like graphite, which gives a ne variation of ohmicvalues.

The bottom of box 32 is provided with a hollow boss 4D having a recess4I to receive the lower end of a shaft 42. An extension 43 on thisshai't projects through cover 33 and carries a knob or other suitablenger piece 44. The radial arm 45 projecting from knob 44 is arranged tomove over the station scale or dial 29. The knob 44 and pointer 45 maybe molded as a single piece of bakelite, ber, hard rubber and the like.The scale 29 carries suitable notations to indicate the variousbroadcasting stations, as is usual in dials on radio receivers. Theshaft 42 is mounted for rotary as well as axial movement, and anexpanding coil spring 46 in the hollow post 49 normally holds the shaftin raised or outer position. The rheostat arm 2I has an annular baseportion 41 adapted to be mounted on one end of a hub 49 fixed on shaft42, and screws or other fastening members 49 may be used to connectthese parts securely together. The hub 48 may be a sepa.-

rate insulating piece attached to shaft 42, or

these two parts may be cast or molded as o. unit. A second contact arm59 having an annular base portion 5I is mounted in a similar manner onthe lower end of hub 48, and the function of this second arm is tooperate with the resistance element I9 for controlling the volume ofreproduction, as I shall explain more fully in due course.

The rheostat arms 2| and 58 are so spaced that only one of them canengage the resistance wire I9 at a time. In the normal raised positionof shaft 42, the lower arm 50 is in contact with resistance I9, as shownin Fig. 3. When the knob 44 is pushed in to close the circuits ofsolenoid coilsA I6 and I8, the station-selecting arm 2| is moved intocontact with resistance I9, as shown in Fig. 6. The pointer 45 indicatesnot only the selected station, but is also used to indicate roughly thedegree of loudness of the reproduction. Referring to Fig. 2, theloudspeaker volume is a minimum when the pointer 45 is at the left andgradually increases as the knob 44?. isturnedfv clockwise. One of theblocks 31 supports a. pair of insulated spring fingers. 52l and A53.`arranged to bear.l against the hub portions. 4.1.E andl 5I. ofv rheostatarms 2.I: and For. convenience of manufacture, each of thesearmsandzitshubfpor.-

tion may be stamped or pressed from. sheet-brass. 'Ehe pressure.

55, which may bea. spring blade secured at one,

end. by screws 56. or otherwise. The free'end of springV arm. isadapted' to engage a xed contact 51 carried by a bracket or projection58. They sWitch-supportingparts 54.and.58. may be formed integral with.the body of thebox if the latter is molded of insulating compositionmaterial. The normal set.` or. tension. of. spring arm 55 is such thatits free end. is outof engagement with contact 51. The extension. 43of?` shaft 4-2 passes through a hole in switch arm 5.5 and the spring islocked to the shaft by a cross-pin` 59. and the. shoulder 60. Thisconnection between switch arm` 55-.and shaft 42. permitsrotation of theshaft without affecting theposition of the switch arm. However., whenthe knob 44 is pushed in, the` switch. arm 55 is pressed into engagementwithy contact 51. The switch army 55 need not. be resilient, because theshaft. 421 is normally maintained in raised or outermost position bythe` expanding coil spring 48. On the otherl hand, the spring 45 maybeomitted by making the switch. arm 55. sufciently resilient toholdv theshaft 4.2 in raisedx position.. The purpose. of switch 55.-51 is toclose the circuit through solenoid coil I6 when. the knob 44 is pushedin. This will be understood. when I-l describe the wiring diagram. of,Fig. 13.` However., as I shall subsequently explain, the. switch55--511nay be omitted and replacedbyarelay switch inaradio receiver.

T hecover 330i-:box 32 has arwindow 6I which isv closed by, atransparentv or. translucent strip 62 of glass, Celluloid, netting,mica, oiled. skin or the like. A Simple; way to holdthe strip.62 inplace isl to insertatheside edges.- iny slots 63 formed inthe. insidelof; cover 33; andi a. set-.screw 6,4.locksthestripin position. Thiswillv be understood by `lookngat Fig. 7*. Below the window 6I. isasrnallfelectriclamp 6 5-mounted1in a metal socket 68, which, isAcarriedby. a flange 8.1.. de-

pending fromcover 3 3: A; screw. pisfin good electrical Contact;A withsocket 56:; and serves as a binding post fora conductor. 6.9.The-.central contact of lamp =,I55 bears against a spring vfinger w 1I)vsecured by a screwv 1I to a.V projection 34' on the annular cover ange3,4. The` screw 1I may alsobe used as a bindingpostfor a conductor 12,The signal lamp 65, may be Supported'in any other practical Way in box32,` but-the mounting just olescrloedV is Simple andi permits. easy inintharadio-receiveryison. Asglshcwn-VinFig.2,V

sertionandremoval ofythe lamp after the cover 33l is taken off; Whilethe lamp I5'4 is. not absoq lutely necessary, Ythe llight shining.through` Window 6I tells-the operator that the` electric power thewindow 5I issowide thatitcan .notr b e fully covered by the.rotarypointer.- 4 5.'V A, suitable switch 13 in 3.2.:is9ntrc11edby. a fingerpice 14 egiinsthrcugb aslqt. 15@ wver toturnthe electric powerfintheradioreceiver on, and off. It. will not be necessary toshow or describethemechanism of switch 13, because many` types of switches can beobtained in the market;

with a. worm gear 18, which drives the tuning.

shaft at properly reduced speed. It is assumed; that: the tuning shaftI2 is automatically reversed. when the indicator in the receiver cabinetis at either end of the. scale, which usually extends over an arc. of180.degrees. The automatic reversal of shaft I2 may be accomplishedeither by a reversing switch if the motor I0 is reversible, or bytransmission connections interposed between gear wheel 18. and shaft I2for changing the continuous rotation of the gear into alternatelyopposite movements of the tuning shaft. In Fig. 8 the rectangularoutline 19 indicates diagrammatically any practical'mechanism forautomatically reversing the rotation of tuning shaft I2 at eachv end of:the dial. For an example of an automatic reversing mechanism suitable inthis connection, I refer to my copending application Serial Number338,391, filed February 8, 1929. By. letting the motor shaft run in onedirection only, it is. possible to use a universal motor. adapted tooperate equally well on direct current andv alternating current.

The driving connections between the` electric motor I0 and tuning shaftI2. are such that the latter maybe turned by a. hand knob on the frontpanel BI of the radio cabinet. The knob is connected to a stub shaft 82which carries a pinion` 83 arranged tc mesh with a gear wheel 84`xed onshaft I2. The resistance element I5 of rheostat R may be mounted on theinner wall of front panel 8|, and the contact arm I4 is mounted;directly on the tuning shaft I2. However,.in the broader aspect of myinvention, the

rheostat; arm I4.may be supported independently of shaft I2 andoperatively connected thereto in any practical way. In the presentinstance I have shown the resistance element I5 as a fine wire woundv ona exible insulating strip 85 which is attached. at. its projecting endsto a block 86, and this block is secured to the inner face of panel 8|by bolts or screws 81. The block 86 is provided with an extension 88. towhich a spring finger 89 is attached. The free end of finger 8B bearsconstantly against the hub portion 90 cf rheostat arm I4; I mightexplain here that when I- speak of'shaft. I2 as the tuning shaft, I donot meany that the tuning elements I3 must be mounted thereon, but Imean any shaft operable to adjust the tuning means of the receiver.

An insulating frame indicated as a whole by 9I;is secured to the bottom92 of the radio cabinet` by screws. 93 or otherwise. The solenoid coilsIBand ISare mounted in openings or recesses 94:. in frame 9i, whichmayconveniently bev moldedin onepiece of bakelite, hard rubber, fiber andthe like. The pivot pin24 of lever 23 ismountedin a pair of cross-pieces95 on frame 9I. The lever 23may be a flat bar mounted on These00111180'.

tom of frame 9|. The reciprocable magnetic core 22 has a slot 99 for thepassage of lever 23, which is connected to the core by a pin |00. Thelever 23 has a. short longitudinal slot |0| to provide the necessaryloose play between the re.- ciprocable core 22 and the pivotal movementsof the lever. The magnetic core 22 moves in and out of coils I6 and |8so freely that the tensioned spring 21 quickly restores the lever 23 tonormal position when the coils S and I8 are deenergized orcounterbalanced. The contact 25 may be a short leaf spring attached tolever 23 in any suitable way, as by being inserted in a small block 23'which is secured to the upper end of the lever. The stationary contact25 is a U shaped member (for example, a piece of bent brass) set in arecess |02 in frame 9| and held in place by a screw |03, which may alsobe used as a binding post.

The insulating frame 9| has a hole or recess |04 in which a coil |05 andmagnetic core |05 are mounted. A pair of spaced ears or lugs |01 onframe 9| support a rod or pin |08 which carries a depending hinge |09.This hinge is a magnetic member or else carries an armature ||0 inoperative relation to the outer end of magnetic core |05. A switch arm||2 attached to hinge member |09 is adapted to engage a contact ||3mounted on frame 9|. The contact ||3 may simply be the head of a screwor bolt inserted in a hole |4 in the frame, A tensioned torsional spring|5 on hinge pin |08 normally holds the armature ||0 away from magnet|05, so that the switch arm 2 hangs in open position. When the coil |05is energized, the armature 0 is attracted and the switch arm ||2 ismoved into engagement with the stationary contact 3.

The operative connections between the remote control box and the radioreceiver are diagrammatically indicated in Fig. 13, which will now bedescribed. Two service mains |6 and ||1 lead from a plug ||8 adapted tobe inserted in an ordinary house-lighting socket. If necessary, acurrent rectier ||9 may be interposed. A suitable hand-switch |20 isinserted in lead ||6 to turn the electric power on and oi for allcircuits in the radio receiver and remote control box. The switch |20may be of any suitable construction and is usually operated from thefront panel of the radio receiver. Two conductors 2| connected in shuntacross switch |20 and the power supply are supposed to be properlyconnected to the receiver system to supply the necessary power, as willbe understood without further explanation. The service mains ||6| l1lead to a suitable voltage reducer |22 for cutting the house-lightingvoltage down to an amount low enough for operating the electric motorI0, the differential coils |6 and |8, and the relay coil |95. As a rulethat voltage need not be more than ten volts and probably less. The lowvoltage conductors leading from the reducing device |22 are indicated at|23 and |24. A wire |25 connects the movable switch contact 26 withconductor |23. The associated fixed contact 25 is connected to oneterminal of the electric motor I0 by a wire |26, and the other motorterminal is connected by a wire |21 to the low voltage lead |24. I mayinterpose a clutch coil |28 which operates a clutch member when the coilis energized to connect the motor shaft with the tuning shaft |2. Whencoil |28 is de-energized, the clutch connection between the motor andthe tuning shaft is broken, so that the tuning shaft stops instantlywhen the motor circuit is interrupted.

A wire |29 connects the contact finger 89 of rheostat R to conductor |24and the associated resistance element l5 is connected by a Wire |30 toone side of coil I6. The other side of this coil is connected by a wire3| to the switch arm 55 in the remote control box. One side of the otherdii'erential coil I8 is connected by a wire |32 to conductor |23, andthe other side of this coil is connected by a wire |33 to resistanceelement |9 in the remote control box. A pair of wires |34 and |35leading from service main H6 are connected to switch members ||2| I3, sothat the latter are shunted across the hand-switch |20 in the radiocabinet. The relay coil |05 is connected at one side bya Wire |36 to amovable switch arm |31, and the other side of the coil is connected towire 12 which leads to one terminal of signal lamp E5, as previouslyexplained. A stationary contact |33 associated with switch arm |31 isconnected by a wire |39 to the low voltage conductor 23. A pivoted cammember |40 operated by the nger piece 14 moves the switch arm |31 toopen and closed positions.

rlhe parts 31, |38 and |40 may be assumed to represent the switch 13mounted in the remote control box, but any other practical form ofswitch may be used. The contact nger 52 in the remote control box isconnected by a wire |4| to conductor |24, and the other contact finger5S is connected by a wire |42 to one side of coil |43. The other side ofthis coil is connected by a wire |44 to wire 433. The coil |43 is thesecondary coil cf an audio-frequency transformer |45 in the radioreceiving system. The rheostat resistance I0 is shunted across thesecondary coil |43, so that by varying the resistance it is possible tovary the volume of reproduction.

When the iinger piece 14 is moved to on position, switch |31|38 isclosed and relay coil |55 is energized to close the power switch 2| i3,whereby the radio receiver is connected to the source of electric powersupply. Since the lamp E5 is connected in series with relay coil |05,the lighting of the lamp tells the operator that the electric power forthe radio receiver is on. It may be advisable to shunt a resistance |46around the lamp, so as not to disorganize the remote control apparatusif the lamp should happen to burn out. The operator turns knob 44(Without depressing the same) until the pointer 45 indicates the stationwanted. As long as the arm 2| is out of, Contact with resistance I9, thecircuits of coils 6 and 8 are open and the motor l0 is not running.However, when the operator depresses knob 44 after having moved it tostation-selecting position, the engagement of contact arm 2| withresistance element i9 closes the circuit of coil I0 as follows:Conductor |23| wire |32, coil I8, wire |33, resistance i9, contact arm2|, nger 52, wire |4|, return conductor |24. At the same time, thedepressing of knob 44 (which now operates like a push button) closes theswitch 55-51, thereby closing the circuit of coil |6 through thefollowing connections: conductor |23, wires |39 and |41, contact 51,switch arm 55, wire |3|, coil |6, resistance 4element 5, contact arm |4,nger 89, wire |29, return conductor |24. Unless the station indicated bypointer 45 happens to bein tune, one of the two coils |6 and I8 willpredominate in its electroemagnetic effect on the movable core 22, sothat the latter will be drawn into the predominating coil and the con`tact 25 will be moved against contact 25.

'I'hecircuit of motor I0 is now closed, as follows:v Conductor |23, wire|26, through windings Yof motor l0. clutchA coil |28 (if the same isused),

and through wire |21 to return conductor |24. The energized motor drivesthe tuning shaft |2 and with it the contact arm |4 until the latter isin such position that the electromagnetic ef.- fect of coil I6 issubstantially equal to that of the opposing coil I8, whereupon themagnetic core 22 moves to neutral position and opens the motor switch25-26. The tuning shaft stops instantly in position for the stationrepresented by the indicator 45 on the remotecontrol box. l It takesonly .a few se-conds for any station to be tuned in, and the operator issupposed to hold the knob or button 44 pushed in until he gets theselected station. When the button is released, the rheostat arm 2| andswitch arm 55 automatically move to open position and the circuits ofcoils I6 and I8 are broken, so that no current is wasted after theselected station has been tuned in The release of button 44 moves thesecond rheostat arm into contact with resistance |9, so .that theoperator may now regulate the' volume of reproduction by simply turning`the 'knob 44. one way or the other. If a, person wants. to hunt .for a`suitable program. withoutcaring Yfrom what station it emanateshe,pushes the knob 44 and turns it either Way from one end of the scale tothe `other until he .gets the kind of broadcasting he li-kes.l The knob44 is then released and the loudspeaker volume is adjusted by turningthe pointer 45 toward lloud or soft position. Shoulders 36..on strip 36engage the arm 2| to :limit the rotation of knob 44 to half a revolutionbetween the 0. v and 100 marks on the dial. Y

I-f 4the'wires 42 and |44 `areso connected in the receiver system as tocarry Aa relatively high, volt- ,age,I may substitute .the volumecontrol .arrangement shown diagrammatically in Fig. 14 whereV ayseparate rheostat R2 is shunted across the sec- 1ondary .coil |43. Thisrheostat ,comprises a resistance element .|48 connected by a wire |49 to.one lside -of lcoil |43, ,and .a -pivoted contact `arm |56 `connectedby ,a wire |51 to .the other side `of the coil. The contact arm r|50 isconnected to a reciprocable .solenoid .core orplunger |52, .which isvoperatively Aassociated with .a .coil |53. This .coil is controlled,bya rheostat R3 comprising a resistance element |54 .and a rotarycontact |55.

f The source -of .electric energy for coil |53 Ais dialgranimatieallyindicated by a battery |56, but .in actual .practice the -coil isconnected to the low voltage conductors .|.23-I24 of Fig. 13. AAcontracting coil spring |51 normallyholds the.plung -er'l53 in :raisedposition, so 'that the contactarrn |50 `is .in position |50' .forminimum volume .of

reproduction.

When thecoil |53 is energized, the movement of plunger |52- depends;uponthestrength of current passing .through the `coil `asrletermined .by

the positioneoifrheostat arm |55. When vthe lat- Y ter is in loudgposition'as shown in Fig. 14, the current through coil |53 is a maximumand the plunger ;|52 is drawn farthest finto the coil to move thecontact arm i|'to theifull `line position -|'50,:sothat practically allthe resistance |48 is 'included'infcircuit .'Consequently, the'volume ofreproductionis now amaxirnum. For any intermediate position 'of contactarm |55 betweenthe extreme `rloud and softjpositions, the solenoid`|52|53will move the 'contact arm v| 56 to a corresponding position onresistance `element |48,

so that the volume of reproduction will roughly corresponding to theposition of controlling arm |55. It is understood thatthe rheostat arm|55 is operated by the knob 44, the same as contact arm 50. Whilethevolume control system of Fig. 14 requires an additional rheostat andsolenoid in thel radio cabinet, it has the practical advantage that thecoil |53 is connected in a circuit of low voltage.

The switch 55-51 in the remote control box can be eliminated and thecircuit of coil I6 controlled by a relay switch in the radio receiver.IThis alternative arrangement is diagrammatically illustrated in Fig.15, where only so much of Fig. 13 is shown as is necessary to understandthis modification. Corresponding parts in Figs.

13 and 15 are indicated by like reference numerals. The coils i6 and |8in Fig. 15 are mounted on a magnetic core or frame |58, and the movableswitch .contact 26 is in the form of. a spring arm carrying an armature|59 adapted to be attracted to the magnetized core |58 when eithercoilpredominates. The conductor |33 of coil |8 contains a relay coil |60mounted on a magneticcore |6I. Oneside of coil 16 is Vconnected by aWire |62 to a movable switch arm |63, which may simply be a spring bladenormally held away from the associated .contact |64. The spring bladev`|63 either is magnetic or carries an armature |65 arranged to beattracted to core |6| when `coil |66 is energized for closing thecircuit of coil I6. In other words, when the knob or push -button 44 ofthe remote control box Vis pushedin after a station has been selected,the relay |66|| is energized to close the circuit .of the opposing coilI-6.

Still referring to Fig. 15, as long as y.either .of the differentialcoils |6 and I8 predominates electromagnetically, the core |58 isenergized to hold the switch arm 26 in closed position, thereby causingthe electric -motor I6 to drive the tuning shaft |2, as previouslyexplained in connection with Fig. 13. When Ythe shaft is in selectedtun- `ing position, the Aopposing magnetic fields Vproduced in core |58are substantially balanced or neutralized, vand the switch member 26automati- .cally vmoves vto open position. The use of the -by anequivalent resistance |56. Otherwise, what has been said for theoperation -of-the system in Fig. 13, applies to Fig. l5. It isunderstood that Fig. 15 is intended to be substituted inFi g. 1-3 for`switch 55,-5! and reciprocable :core l.2.2.

It will be clear frorn the foregoing description that I have provided asimple apparatus for the -complete.controlof a radio receiver atadistance,

including notonly the selection of a desired kstation, but also theregulationof loudspeaker vvolume and turning the electric :power yforthe receiveron and off. Not more vthan six or seven Vwires .of lowvoltage are required in the electric cable .that connects the remotecontrol boxwith the radio cabinet. vIn Fig. 13 the imaginary adottedline ,|61 is supposed to cut through the c ablefzso that `the linescrossing it are `the uwires 70 that compose the cable. The low voltageof the cable Ywires makes it absolutely safe to use a cable of anyYlength without special insulation. Thel use `of mresistance li-)forselecting astation and 'regulating the loudspeaker volume simplifiesthefl mechanism inside the control box, which can be made very small andlight.

Although I have shown and described certain specific constructions, Iwant it understood that my invention is not limited to the details setforth. It is to be expected that changes and modifications will probablyoccur to those engaged in building a remote control apparatus in accord-.ance with my invention, without departing from the scope of theappended claims.

I claim as my invention:

1. A radio receiver having variable tuning elements and a loudspeaker,in combination with a station-selecting device having a rotary fingerpiece, means for holding said nger piece against lateral tilting, a pairof rotary members simultaneously operated by rotation of said ngerpiece, said members being separate from said tuning elements, meanscontrolled by one of said members for selecting a station to be tunedin, means controlled by the rotary movements of the other member forregulating the volume of said loudspeaker while the tuned-in stationremains in tune, and means for so mounting said nger piece that itremains in any adjusted volume-control position when released.

2. In a tuning device for radio receivers, the combination of a rotaryknob mounted so that it can be pushed in, means whereby said knobremains in any rotatably adjusted position when released, spring meansfor normally holding said knob in outermost position and automaticallyrestoring it to normal position upon manual release thereof, electricmechanism controlled by the rotation of said knob in depressed positionfor selecting a station to be tuned in, said mechanism including anelectric circuit, switch means controlled by the return movement of saidknob for opening said circuit, an electric device for regulating theloudspeaker volume, and means operated by the rotation of said knob innormal position for controlling said device independently of saidmechanism, which remains in selected tuning position during theoperation of said volume-controlling means.

3. A remote tuning box for radio receivers having means for selecting astation to be tuned in, means for controlling the volume of reproductionof a tuned-in station, said two means including a pair of separatecontact members and a variable resistance element common to bothmembers, and means whereby said volume-controlling means operatesindependently of said station-selecting means which remains in selectedtuning position during the operation of the volume-controlling means.

4. A remote control device for radio receivers comprising a singleadjustable knob capable of rotary movement in either direction, meansfor holding said knob against lateral tilting, stationselecting meansoperable by rotation of said knob, volume-control means also operable byrotation of said knob, the degree of volume depending upon the variableangular position of the knob connections whereby said station-selectingmeans and volume-control means are simultaneously operated by said knobbut only one of said means is in operative condition at a time, andmeans whereby said knob remains in any rotatably adjusted position whenreleased.

5. In radio receiving apparatus having tuning mechanism and aloudspeaker, the combination of a variable electric resistance element,operative connections between said element and said mechanism for tuningin a selected station by varying the resistance of said element, otheroperative connections between said element and said loudspeaker forregulating the loudspeaker volume by varying the resistance of saidelement, and means for controlling either of said connectionsindependently of the other.

6. The combination of a radio receiver having a tuning shaft and aloudspeaker, a rotary spindle' mounted to occupy two different axialpositions, means for holding said spindle against lateral tilting, aknob on said spindle, means controlled by the rotation or said knob inone axial position for operating said tuning shaft to bring in a desiredstation, means controlled by the rotation of said knob in its otheraxial position for regulating the volume of said loudspeaker connectionswhereby said tuning means and volume-control means are simultaneouslyoperated by said knob but only one of said means is in operativecondition at a time, and means whereby said shaft remains in selectedtuning position during the operation of said volume-controlling means.

7. A radio receiver having variable tuning elements and a loudspeaker,electric mechanism for operating said elements, and a device forregulating the volume of said loudspeaker, in combination with a remotecontrol box having a manually operable rotary shaft mounted for axialadjustment to two operative positions, means for preventing lateralmovement of said shaft, electric connections controlled by the rotationof said shaft in one axial position for operating said mechanism to tunein any selected station, electric connections operated by the rotationof said shaft in its other axial position to control saidvolume-regulating device independently of said tuning connections, sothat the selected station remains in tune during the volume-regulatingoperation, and means whereby said shaft remains in any rotatablyadjusted position when released.

8. A remote tuning box for radio receivers having a variable resistanceelement, a movable contact arm arranged on one side of said element forselecting a station, a second movable contact arm arranged on the otherside of said element for controlling the volume of reproduction, acommon adjustable support for said arms, only one of said arms beingnormally in engagement with said element, and a finger piece for movingsaid support out of normal position to a second operative position so astc bring the other arm into engagement with said element, said supportbeing also adjustable by said finger piece to move either contact armalong said element to predetermined position.

9. A remote tuning device for radio receivers having a resistanceelement, two adjustable contact members associated with said element,manually operable means for adjusting said members in relation to saidelement, one of said members cooperating with said element to controltuning mechanism in the receiver, the other member cooperating with saidelement to control the volume of reproduction, and means for so mountingsaid members that only one at a time engages said element.

l0. In a remote tuning box adapted to be operatively connected with aradio receiver, a rheostat comprising a resistance element and a pair ofcontact arms, a rotary shaft on which said arms are mounted in such away that only one arm at a time can engage the resistance element, oneof said arms being adjustable to select a station to be tuned in by thereceiver. the other arm being adjustable to regulate the volume ofreproduction, and a spring support for said shaft to permit axialmovement thereof, said support normally holding the volume-control armin contact with the resistance element.

11. Electric driving mechanism which includes an electromagneticcontrolling device comprising a pair of coils in magnetically opposedrelation, one of said coils being controlled by said mechanism, incombination with a remote control box having manually adjustable meansfor controlling the other coil of said device, a pair of normally openswitch members in said box, each switch member being connected in thecircuit of one of said coils, a nger piece on said boX for closing bothof said switch members, means whereby said iinger piece when releasedautomatically opens said switch members, and electrical connectionswhereby said mechanism is operative as long as either coil predominatesin said electromagnetic device, said mechanism stopping when theelectromagnetic effects of said coils are substantially balanced.

12. Electric driving mechanism which includes as electromagneticcontrolling device comprising a pair of coils in magnetically opposedrelation, a rlieostat operated by said mechanism for controlling one ofsaid coils, in combination with a remote control box having a normallyopen switch in the circuit of each coil, a manually adjustable rheostatfor selectively controlling the other coil, and a single finger piecefor operating said rheostat and both of said switches, said mechanismbeing operative when either coil prestantially balanced effects.

in their electromagnetic ADOLPI-I A. THOMAS.

